Fiber-reinforced, polymer matrix composites (PMCs) are high-performance structural materials that are commonly used in applications requiring resistance to aggressive environments, high strength, and/or low weight. Examples of such applications include aircraft components (e.g., tails, wings, fuselages, and propellers), high performance automobiles, boat hulls, and bicycle frames.
Composite structural parts for aerospace applications typically include a surfacing film to provide the required performance characteristics to the composite structures prior to painting. These surfacing films are used to improve the surface quality of the structural parts while reducing labor, time and cost. The surfacing films are usually co-cured with the fiber-reinforced polymer matrix composite materials during the manufacturing of the structural parts. Conventional epoxy-based composite prepregs and surfacing films exhibit poor resistance to electromagnetic energy (EME) events, such as lightning strike (LS), electrostatic discharge (ESD), and electromagnetic interference (EMI) due to their insulative properties. The relatively high resistivity (low electrical conductivity) exhibited by epoxies inhibits the energy of a lightning strike from dissipating adequately, resulting in skin puncture and delamination of the underlying composite structure. Further, the charge generated on the surface of the composite can remain for long periods of time, elevating the risk of ESD in low relative humidity environments that can damage electronic systems and risk sparking in the vapor space of fuel tanks. Additionally, the poor electrical conductivity of epoxy-based surfacing films may inhibit the mobility of charge carriers, which can impair the ability of the composite structure to provide EMI shielding. To minimize the damage of lightning strike on a composite structure, there is a need for enhancing the electrical conductivity of the composite structure to provide LS/ESD/EMI protection for composite parts on aircraft. It is not desirable, however, to incorporate conductive material that will significantly increase the overall weight of the aircraft. Furthermore, conventional surfacing films are not very resistant to commercial paint stripping solutions, such as benzyl alcohol-based solutions, for paint-stripping purposes. Those paint strippers can cause swelling and/or blistering of the surfacing film, thereby making the re-painting process more cumbersome. As such, there exists a need for a multifunctional, conductive surfacing material that is light-weight, can withstand repeated paint stripping using conventional paint stripping solutions, and can also withstand exposure to ultra-violet (UV) radiation.